Jared Lee Loughner took full responsibility for the Arizona massacre, and now faces the rest of his life in prison. NBC's Miguel Almaguer reports.

By Pete Williams and Isolde Raftery, NBC News

The federal Bureau of Prisons psychologist observing Jared Loughner concluded in an April report released Thursday that he was mentally competent to stand trial for the Arizona shooting spree that left six people dead and 13 wounded, but there was no guarantee he would remain so given his fragile state.

Christina Pietz also concluded that Loughner’s status "may wax and wane" and could seriously worsen under the pressure of a trial.

Her assessment is part of what led his lawyers to conclude that a guilty plea was the wisest move.

Loughner opened fire on Jan. 8, 2011, outside a Tucson Safeway where former Rep. Gabrielle Giffords was holding a meet-and-greet with constituents. Six people, including a federal judge, John Roll, and a 9-year-old girl, Christina-Taylor Green, were killed. Giffords, who was shot in the head, was among 13 people wounded. Loughner pleaded guilty on Tuesday and in doing so, avoided the death penalty.

The report released Thursday covers a roughly 12-week period during which Pietz evaluated Loughner, from January to April of this year, at the U.S. Medical Center for Federal Prisoners in Springfield, Mo. Loughner was sent there after initially being found incompetent to stand trial.

In the 11-page report, which was included in a court filing, Pietz concludes that Loughner is schizophrenic, but that his symptoms can be controlled with medication.

Throughout, the psychologist details Loughner’s housing and daily routine. Because he is a high-profile inmate, she writes, he is housed in a two-room area of the facility. One side of his room has a writing desk, bed and shower. The shower doesn’t have a curtain to allow staff to monitor him.

In that room, he keeps a television, pen, toothpaste, toothbrush, shampoo and towel. The other room has stationary bike, although Pietz writes that Loughner rarely uses the second room.

Loughner remained on suicide watch during the 12 weeks Pietz evaluated him, and guards recorded his activities every 15 minutes in a suicide watch log.

“He denied experiencing auditory hallucinations,” Pietz wrote. But “there were a few times that staff suspected he was attending to internal stimuli because he would moan while pacing in his room.”

Loughner attended a therapy group with four other inmates from whom he was separated with a mesh wire. Pietz reported that he was an active participant during most of those sessions but sometimes paced in his area.

Loughner also asked for a job and received two: rolling towels and stamping returned addresses on blank envelopes.

His improvement over time was marked, Pietz wrote, and when he spoke with her, he remained focused. During those conversations, which he knew would likely become public, Loughner sometimes said he regretted that Giffords did not die.

“He talked openly about his disappointment that Rep. Giffords could be alive,” Pietz wrote. “When I asked what this meant he stated, ‘That I failed. I’m not an assassin. That I ruined my life for nothing. I think differently now.’”

Later in the interview, he told Pietz, “It’s another failure if she’s alive. Jared Loughner failed again. He’s a failure. So all of this would be for nothing.”

On Jan. 24, the beginning of his evaluation, Loughner said, “I saw her on TV last night. I saw Christina Green. I saw Mrs. Hileman (Suzi Hileman, a shooting survivor). I saw the guy that held me down. I saw her walk into her office for the last time. She was going to the State of the Union address. I swear to you that’s not the woman I shot. The woman I shot in the head died instantly. No one could survive that gunshot wound to the head.”

Later though, Loughner demonstrated to Pietz that he understood Giffords was alive.

Pietz reported that his attorney visits left Loughner exhausted. At first, he was unrestrained during those meetings. But after he spat and lunged at one of his attorneys, he was outfitted with a belly chain, handcuffs and leg irons. Those restraints have since come off.

In conclusion, Pietz writes: “Because Mr. Loughner’s condition may wax and wane, I recommend the court expeditiously address issues related to his situation.”

After his guilty plea, Loughner was returned to the Missouri facility pending sentencing on Nov. 15. He faces a sentence of life in prison.